July 2011

I remember reading as a kid in my 3-2-1 Contact Magazine that there were theories then that automobile exhaust could increase snow and rain near urban centers - it's interesting to think about how human activity can change even short-fused weather events.

BOULDER--Researchers have found that areas near commercial airports sometimes experience a small but measurable increase in rain and snow when aircraft take off and land under certain atmospheric conditions.

The new study led by the National Center for Atmospheric Research (NCAR), is part of ongoing research that focuses on so-called hole punch and canal clouds that form when planes fly through certain mid-level clouds, forcing nearby air to rapidly expand and cool. This causes water droplets to freeze to ice and then turn to snow as they fall toward the ground, leaving behind odd-shaped gaps in the clouds.

The research team used satellite images and weather forecasting computer models to examine how often this type of inadvertent cloud seeding may occur within 62 miles (100 kilometers) of six commercial airports: London Heathrow, Frankfurt, Charles De Gaulle (Paris), Seattle-Tacoma, O’Hare (Chicago), and Yellowknife (Northwest Territories, Canada), as well as Byrd Station in Antarctica. They found that, depending on the airport and type of plane, the right atmospheric conditions typically exist up to 6 percent of the time, with somewhat more frequency in colder climates.

The lead author, NCAR scientist Andrew Heymsfield, says this phenomenon likely occurs at numerous other airports, especially in mid- and high-latitude areas during colder months. The key variable is whether there are cloud layers in the vicinity that contain water droplets at temperatures far below freezing, which is a common occurrence.

He adds that more research is needed before scientists can determine whether the precipitation produced by this effect is significant. The inadvertent cloud seeding may increase the need to de-ice planes more often, he adds.

“It appears to be a rather widespread effect for aircraft to inadvertently cause some measureable amount of rain or snow as they fly through certain clouds,” Heymsfield says. “This is not necessarily enough precipitation to affect global climate, but it is noticeable around major airports in the midlatitudes.”

The researchers did not estimate the total amount of rain or snow that would result from such inadvertent cloud seeding. However, they analyzed radar readings that, in one case, indicated a snowfall rate of close to an inch an hour after several planes had passed through.

The study is being published this week in the journal Science. Researchers from NASA Langley Research Center and the University of Wyoming, Laramie, co-authored the paper. Funding came from the National Science Foundation, which is NCAR’s sponsor, and from NASA.

-----Solving a cloud mystery----

Scientists for decades have speculated about the origins of mysterious holes and canals in clouds. Heymsfield led a study last year establishing that the gaps, which sometimes look as though a giant hole punch was applied to a cloud, are caused when aircraft fly through midlevel clouds that contain supercooled droplets.

When a turboprop plane flies through such a cloud layer with temperatures about 5 degrees Fahrenheit or lower (about -15 degrees Celsius or lower), the tips of its propellers can cause the air to rapidly expand. As the air expands, it cools and causes the supercooled droplets to freeze into ice particles that evaporate the droplets and grow, falling out of the clouds as snow or rain.

Jet aircraft need colder temperatures (below about -4 to -13 degrees F, or -20 to -25 degrees C) to generate the seeding effect. Air forced to expand over the wings as the aircraft moves forward cools and freezes the cloud droplets.

The effect is unrelated to the trails of condensed water vapor known as contrails made by the exhaust of jet engines.

In the new research, the study team used cloud measurements taken by the NASA CALIPSO satellite to quantify how often such conditions exist within about 62 miles of several airports located in relatively cloudy areas. They chose the 62-mile radius because that is approximately the distance it takes for a commercial aircraft to climb above about 10,000 feet, where many of the supercooled cloud layers are located.

Of the major, mid-latitude airports studied, they found that the Frankfurt, DeGaulle, and O’Hare airports most frequently experienced the right conditions for propeller aircraft to generate precipitation. In each case, the conditions existed more than 5 percent of the time over the course of a year. The researchers found that the right conditions existed more than 3 percent of the time for jets at Heathrow, Frankfurt, and Seattle-Tacoma.

Yellowknife experienced such conditions more often, about 10 percent of the time for propeller planes and 5 percent for jets, presumably because of colder cloud conditions at higher latitudes. Byrd often experienced the very cold conditions that enable jets to cause inadvertent cloud seeding.

The researchers also found that a diverse range of aircraft can induce precipitation. By comparing observations of hole-punch and canal clouds made by a National Oceanic and Atmospheric Administration (NOAA) satellite with flight path records from the Federal Aviation Administration, they confirmed that commercial jets (such as Boeing 757s and the McDonnell Douglas MD-80 series of jets), military aircraft (B-52s), various regional and private jets, turboprops, and prop/piston planes all can induce precipitation.

“It appears that virtually any airplane that flies through clouds containing liquid water at temperatures much below freezing can cause this effect,” Heymsfield says.

Satellite readings analyzed by the team showed that holes and canals generated by aircraft can occur with some frequency. For example, an extensive cloud layer over Texas on January 29, 2007, contained 92 such gaps, some of which persisted for more than four hours and reached lengths of 60 miles or more.

Heymsfield and his colleagues also used a powerful software tool, known as the Weather and Research Forecasting model, to learn more about how the holes form and develop. They found that the hole rapidly spreads about 30 to 90 minutes after an aircraft passes through. This would be the peak time for precipitation associated with the cloud-seeding effect. After about 90 minutes, ice and snow begin to dissipate.

The University Corporation for Atmospheric Research manages the National Center for Atmospheric Research under sponsorship by the National Science Foundation. Any opinions, findings and conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

An interesting article from the University of Alabama at Huntsville, regarding research done in their Earth System Science Center:

HUNTSVILLE, Ala. (July 26, 2011) -- Data from NASA's Terra satellite shows that when the climate warms, Earth's atmosphere is apparently more efficient at releasing energy to space than models used to forecast climate change have been programmed to "believe."

The result is climate forecasts that are warming substantially faster than the atmosphere, says Dr. Roy Spencer, a principal research scientist in the Earth System Science Center at The University of Alabama in Huntsville.

The previously unexplained differences between model-based forecasts of rapid global warming and meteorological data showing a slower rate of warming have been the source of often contentious debate and controversy for more than two decades.

In research published this week in the journal "Remote Sensing"http://www.mdpi.com/2072-4292/3/8/1603/pdf, Spencer and UAHuntsville's Dr.Danny Braswell compared what a half dozen climate models say the atmosphere should do to satellite data showing what the atmosphere actually did during the 18 months before and after warming events between 2000 and 2011.

"The satellite observations suggest there is much more energy lost to space during and after warming than the climate models show," Spencer said. "There is a huge discrepancy between the data and the forecasts that is especially big over the oceans."

Not only does the atmosphere release more energy than previously thought, it starts releasing it earlier in a warming cycle. The models forecast that the climate should continue to absorb solar energy until a warming event peaks.Instead, the satellite data shows the climate system starting to shed energy more than three months before the typical warming event reaches its peak.

"At the peak, satellites show energy being lost while climate models show energy still being gained," Spencer said.

This is the first time scientists have looked at radiative balances during the months before and after these transient temperature peaks.

Applied to long-term climate change, the research might indicate that the climate is less sensitive to warming due to increased carbon dioxide concentrations in the atmosphere than climate modelers have theorized. A major underpinning of global warming theory is that the slight warming caused by enhanced greenhouse gases should change cloud cover in ways that cause additional warming, which would be a positive feedback cycle.

Instead, the natural ebb and flow of clouds, solar radiation, heat rising from the oceans and a myriad of other factors added to the different time lags in which they impact the atmosphere might make it impossible to isolate or accurately identify which piece of Earth's changing climate is feedback from manmade greenhouse gases.

"There are simply too many variables to reliably gauge the right number for that," Spencer said. "The main finding from this research is that there is no solution to the problem of measuring atmospheric feedback, due mostly to our inability to distinguish between radiative forcing and radiative feedback in our observations."

For this experiment, the UAHuntsville team used surface temperature data gathered by the Hadley Climate Research Unit in Great Britain. The radiant energy data was collected by the Clouds and Earth's Radiant Energy System(CERES) instruments aboard NASA's Terra satellite.

The six climate models were chosen from those used by the U.N.'s Intergovernmental Panel on Climate Change. The UAHuntsville team used the three models programmed using the greatest sensitivity to radiative forcing and the three that programmed in the least sensitivity.

I'm not sure I've ever seen such a rapid disintegration of a tropical cyclone upon landfall. The hot and dry conditions from the recent Exceptional Drought in Texas contributed to an amazingly fast evaporation of the rain associated with Tropical Storm Don, meaning less than an inch of rain to even the wettest locales, and literally no rain to some areas directly under the storm's track.

Tropical Storm Don has outrun atmospheric wind shear, sits over anomalously warm water, has outrun the dry air he was entraining, and has developed outflow jets on the southeast quadrant and western semicircle. A quick expansion of the central dense overcast resulted Thursday evening, and the storm may strengthen to a 70-75 mph tropical cyclone by late Friday, en route to Padre Island, TX, for a Friday night landfall.

The Taunton, MA, National Weather Service Forecast Office issued a more complete version of yesterday's storm survey of damage associated with Tuesday evening's storms. See last paragraph for definition of a microburst.

* THE INFORMATION IN THIS STATEMENT IS PRELIMINARY AND SUBJECT TO
CHANGE PENDING FINAL REVIEW OF THE EVENT(S) AND PUBLICATION IN NWS
STORM DATA.

...SUMMARY...
THE NATIONAL WEATHER SERVICE IN TAUNTON MA HAS CONFIRMED A
MICROBURST /STRAIGHT LINE WIND DAMAGE/ NEAR WILBRAHAM IN HAMPDEN
COUNTY MASSACHUSETTS ON 07/26/2011.

THE GREATEST CONCENTRATION OF WIND DAMAGE WAS FOUND IN THE TOWN OF
WILBRAHAM. THE GREATEST DAMAGE WAS ALONG AN APPROXIMATELY 2 MILE
LONG PATH WHICH EXTENDED FROM JUST NORTH OF SPRINGFIELD
STREET...ACROSS THE COUNTRY CLUB OF WILBRAHAM...ACROSS FEDERAL LANE
TO JUST BEYOND TINKHAM ROAD. BASED ON TREE DAMAGE...THE STRONGEST
WINDS WERE ESTIMATED TO BE BETWEEN 90 AND 100 MPH. THE WIDTH OF THE
STRONGEST WINDS AVERAGED APPROXIMATELY 250 YARDS...UP TO A MAXIMUM
WIDTH OF
600 YARDS ALONG SPRINGFIELD ROAD. BEYOND THIS CORE OF STRONGEST
WINDS...MODERATE TREE DAMAGE EXTENDED OUT TO AN AVERAGE WIDTH OF
JUST OVER A HALF A MILE.

OUTSIDE OF THIS AREA OF EXTENSIVE DAMAGE IN WILBRAHAM THE TREE
DAMAGE WAS ISOLATED IN NATURE AND ONLY INVOLVED A FEW TREES AT ANY
ONE LOCATION. THIS INCLUDES AREAS OF SPRINGFIELD...CHICOPEE AND
HOLYOKE AS WELL AS WILBRAHAM OUTSIDE OF THE MAIN DAMAGE PATH. TREE
DAMAGE IN THESE ISOLATED LOCATIONS INDICATED WIND SPEEDS OF 55 TO 65
MPH.

THIS INFORMATION CAN ALSO BE FOUND ON OUR WEBSITE AT
WEATHER.GOV/BOX.

FOR REFERENCE...
A MICROBURST IS A CONVECTIVE DOWNDRAFT WITH AN AFFECTED OUTFLOW AREA
OF LESS THAN 2 1/2 MILES WIDE AND PEAK WINDS LASTING LESS THAN
5 MINUTES. MICROBURSTS MAY INDUCE DANGEROUS HORIZONTAL/VERTICAL
WIND SHEARS...WHICH CAN ADVERSELY AFFECT AIRCRAFT PERFORMANCE AND
CAUSE PROPERTY DAMAGE. STRAIGHT-LINE WINDS ARE GENERALLY ANY WIND
THAT IS NOT ASSOCIATED WITH ROTATION...USED MAINLY TO DIFFERENTIATE
THEM FROM TORNADIC WINDS.

Tropical Storm Don formed Wednesday in the southern Gulf of Mexico, sitting off the coast of Cancun and destined for the United States - but the areas where the storm will likely strike need rain desperately.

...NWS METEOROLOGISTS CONDUCTED A SURVEY OF STORM DAMAGE FROM HOLYOKE TO WILBRAHAM IN HAMPDEN COUNTY MASSACHUSETTS...

THE NATIONAL WEATHER SERVICE OFFICE IN TAUNTON MA CONDUCTED A STORM SURVEY FOR THE WILBRAHAM AND SPRINGFIELD AREAS IN HAMPDEN COUNTY MASSACHUSETTS. THIS SURVEY WAS IN RELATION TO THE SEVERE THUNDERSTORMS THAT MOVED THROUGH WESTERN MASSACHUSETTS DURING THE AFTERNOON OF JULY 26 2011.

THE GREATEST CONCENTRATION OF WIND DAMAGE WAS FOUND IN THE TOWN OF WILBRAHAM. THE GREATEST DAMAGE WAS ALONG AN APPROXIMATELY 2 MILE LONG PATH WHICH EXTENDED FROM JUST NORTH OF SPRINGFIELD STREET...ACROSS THE COUNTRY CLUB OF WILBRAHAM...ACROSS FEDERAL LANE TO JUST BEYOND TINKHAM ROAD. BASED ON TREE DAMAGE...THE STRONGEST WINDS WERE ESTIMATED TO BE BETWEEN 90 AND 100 MPH. THE WIDTH OF THE STRONGEST WINDS AVERAGED APPROXIMATELY 250 YARDS...UP TO A MAXIMUM WIDTH OF 600 YARDS ALONG SPRINGFIELD ROAD. BEYOND THIS CORE OF STRONGEST WINDS...MODERATE TREE DAMAGE EXTENDED OUT TO AN AVERAGE WIDTH OF JUST OVER A HALF A MILE.

OUTSIDE OF THIS AREA OF EXTENSIVE DAMAGE IN WILBRAHAM THE TREE DAMAGE WAS ISOLATED IN NATURE AND ONLY INVOLVED A FEW TREES AT ANY ONE LOCATION. THIS INCLUDES AREAS OF SPRINGFIELD...CHICOPEE AND HOLYOKE AS WELL AS WILBRAHAM OUTSIDE OF THE MAIN DAMAGE PATH. TREE DAMAGE IN THESE ISOLATED LOCATIONS INDICATED WIND SPEEDS OF 55 TO 65 MPH.

THIS STATEMENT WILL ALSO BE AVAILABLE ON OUR WEBSITE...WHICH CAN BE FOUND AT WEATHER.GOV/BOX. IT WILL BE LINKED AS THE LATEST PUBLIC INFORMATION STATEMENT NEAR THE TOP OF THE PAGE.

Some hot, but non-record breaking temperatures in New England from Thursday:

Westfield, MA 101

Chicopee, MA 98

Windsor Locks, CT 98

Boston, MA 97

Concord, NH 97

More records will fall Friday, with over a dozen high temperature records in jeopardy, as many communities in Eastern Massachusetts should rise to 100 degrees. Interestingly, while our NECN forecast for Boston as of this writing Thursday night is 101 for Boston on Friday, this still wouldn't be a record for the city, whose second-hottest temperature on record came on July 22, 1926, when the temperature reached 103. The all-time hottest temperature in Boston is 104. So...while we may not break a record in the City, we're *just about* as hot as it gets.

One complex of rain and thunder moving through Northern ME as of this 1:30 PM discussion is moving steadily east-southeast, and though a severe thunderstorm watch was issued in advance of this shortwave distubance, limited surface heating coupled with stratiform cloud formation has limited vertical growth of embedded convective cells and widespread damage is quite unlikely.

Of more importance are cumulus clouds developing over Northern Adirondacks in Northeast NY. This area has 2500-4000 J/kg of CAPE and a surface maximum of moisture convergence associated with a weak lee side trough. A very weak shortwave is dropping southeast from Massena NY and will cross Northern and Central New England between 18Z and 00Z, and may initiate convection in the Northeast New York cumulus field. Any storms that develop will capitalize on available instability - moderate low and mid level lapse rates, surface based lifted indices as low as -9 - to strengthen rapidly. Most likely area for convective initiation is mountain/hilly terrain of Northeast NY and Green Mountains of VT, and mean storm motion will be ESE at 30-40 mph. Keep an eye to the sky and radar, and I'll keep you posted via my Twitter account @MattNoyesNECN and on NECN television, as well. Reports and/or pictures of ongoing/developing storms to me via Twitter are encouraged!